What were the geographic factors that led Portugal to begin its ocean explorations.

I believe the answer is: Portugal did not have a Mediterranean port, so it needed to find a different sea route to Asia.

At that time, portugal's main target destination was a sea route from south east asia which know commonly referred to as Malaka. But they are not the only one that after this route, which is why they faced countries such as spain, british, and netherlands as competitors.